Semiconductor light emitting device and method for manufacturing same

ABSTRACT

A semiconductor light emitting device includes: a support substrate; a metal layer provided on the support substrate; a semiconductor layer provided on the metal layer and including a light emitting layer; a contact layer containing a semiconductor, selectively provided between the semiconductor layer and the metal layer, and being in contact with the semiconductor layer and the metal layer; and an insulating film provided between the semiconductor layer and the metal layer at a position not overlapping the contact layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 13/531,806 filed Jun. 25, 2012,which is a division of U.S. Ser. No. 12/191,659 filed Aug. 14, 2008 (nowU.S. Pat. No. 8,237,183 issued Aug. 7, 2012), and claims the benefit ofpriority under 35 U.S.C. §119 from Japanese Patent Application No.2007-212100 filed Aug. 16, 2007 and Japanese Patent Application No.2008-044239 filed Feb. 26, 2008; the entire contents of each of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor light emitting device and amethod for manufacturing the same.

2. Background Art

In a structure conventionally known as a reflection type semiconductorlight emitting device, a semiconductor layer including a light emittinglayer grown on a growth substrate is laminated with a support substratevia a metal layer so that light emitted opposite to the light extractionsurface is reflected at the metal layer and directed to the lightextraction surface (e.g., JP-A 2004-104086(Kokai)). In such a reflectiontype semiconductor light emitting device, reflectance at the reflectingstructure contributes to increased brightness, and a higher reflectanceis desired.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided asemiconductor light emitting device including: a support substrate; ametal layer provided on the support substrate; a semiconductor layerprovided on the metal layer and including a light emitting layer; acontact layer containing a semiconductor, selectively provided betweenthe semiconductor layer and the metal layer, and being in contact withthe semiconductor layer and the metal layer; and an insulating filmprovided between the semiconductor layer and the metal layer at aposition not overlapping the contact layer.

According to another aspect of the invention, there is provided a methodfor manufacturing a semiconductor light emitting device, including:selectively forming a contact layer containing a semiconductor on asurface of a semiconductor layer including a light emitting layerprovided on a substrate; forming an insulating film on the surface ofthe semiconductor layer to cover the contact layer; selectively removingthe insulating film to expose the contact layer; forming a metal layercovering the insulating film and the contact layer; and laminating asupport with the metal layer, and then removing the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing thecross-sectional structure of a semiconductor light emitting deviceaccording to a first embodiment of the invention;

FIG. 2 is an enlarged view of portion A in FIG. 1;

FIG. 3 is an enlarged schematic plan view showing an example planarlayout of the contact layer and the insulating film in the semiconductorlight emitting device according to this embodiment;

FIGS. 4A to 4C are schematic views showing an example method formanufacturing a semiconductor light emitting device according to theembodiment of the invention;

FIGS. 5A to 5C are schematic views showing steps following FIG. 4;

FIGS. 6A to 6C are schematic views showing steps following FIG. 5;

FIG. 7 is a schematic view showing an example of the semiconductor lightemitting device according to this embodiment, having the contact layerthicker than the insulating film;

FIGS. 8A to 8C are schematic views showing another example method formanufacturing a semiconductor light emitting device according to theembodiment of the invention;

FIGS. 9A to 9C are schematic views showing steps following FIG. 8;

FIG. 10 is a schematic view for describing the positional relationshipbetween the contact layer and the opening inner edge of the insulatingfilm;

FIGS. 11A and 11B are enlarged cross-sectional views schematicallyshowing the principal cross section of the semiconductor light emittingdevice according to the comparative example, having the contact layerformed on the entire surface;

FIG. 12 is a schematic view for describing that the light emitted fromthe main light emitting region is hard to be totally reflected at theinsulating film around the contact layer;

FIGS. 13A and 13B are schematic views showing the principal structure ofa semiconductor light emitting device according to a second embodimentof the invention;

FIGS. 14A to 14D are schematic views showing an example methodmanufacturing the semiconductor light emitting device shown in FIGS. 13Aand 13B; and

FIGS. 15A and 15B are schematic views illustrating an electrode patternon the light extraction surface side in the semiconductor light emittingdevice according to the embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described with reference to thedrawings.

FIG. 1 is a cross-sectional view schematically showing thecross-sectional structure of a semiconductor light emitting deviceaccording to a first embodiment of the invention. FIG. 2 is an enlargedview of portion A in FIG. 1.

The semiconductor light emitting device according to this embodimentcomprises a semiconductor layer including a light emitting layer (activelayer) 4 b laminated with a support substrate 12 via metal layers 11,13. In this semiconductor light emitting device, light is extracted fromthe side opposite to the support substrate 12, that is, from the upperside in FIG. 1.

The light emitting layer 4 b can be illustratively made of anInGaAlP-based multiple quantum well structure. The light emitting layer4 b is sandwiched between an n-type cladding layer 4 a and a p-typecladding layer 4 c having a larger bandgap than the light emitting layer4 b.

An upper current diffusion layer 3 is provided above the n-type claddinglayer 4 a, and a lower current diffusion layer 5 is provided below thep-type cladding layer 4 c. The upper current diffusion layer 3 and thelower current diffusion layer 5 are illustratively made of InGaAlP andserve to allow the current supplied through a bonding pad 15 and abackside electrode (p-side electrode) 14, which is formed on thebackside of the support substrate 12, to diffuse in the in-planedirection.

The bonding pad 15 containing a metal material is provided on the uppercurrent diffusion layer 3 via a contact layer 2 illustrativelycontaining n-type GaAs. A wire for connection to an external circuit,not shown, is connected to the bonding pad 15.

Contact layers 6 and an insulating film 8 are provided between the lowercurrent diffusion layer 5 and the metal layer 11. FIG. 3 shows anexample planar layout of the contact layers 6 and the insulating film 8.

The lower surface of the lower current diffusion layer 5 (the surface onthe side opposite to the interface with the p-type cladding layer 4 c)is a generally flat surface, on which a plurality of contact layers 6are selectively formed. The insulating film 8 is formed on the lowersurface of the lower current diffusion layer 5 at a position notoverlapping the contact layers 6. That is, the surface of thesemiconductor layer including the light emitting layer 4 b on which thecontact layers 6 and the insulating film 8 are formed is generally flat.

As shown in FIG. 3, a plurality of openings 8 a are selectively formedin the insulating film 8, and one contact layer 6 is located in each ofthe openings 8 a. In the example shown in FIG. 3, the planar shape ofeach contact layer 6 is rectangular. However, it is not limited thereto,but can be illustratively circular or polygonal.

The contact layer 6 is illustratively made of GaAs, and is in contactwith the lower current diffusion layer 5 and the metal layer 11 so thatthe electrical connection therebetween has good ohmic characteristics.

The insulating film 8 serves as a reflecting layer by which the lightemitted from the light emitting layer 4 b to the side opposite to thelight extraction surface on the upper current diffusion layer 3 side isreflected toward the light extraction surface. The insulating film 8 canillustratively be a silicon oxide film, silicon nitride film, or siliconoxynitride film having a lower refractive index than the semiconductorlayer including the light emitting layer 4 b.

The metal layer 13 is formed on the major surface of the supportsubstrate 12 on the side to be laminated with the metal layer 11, andthe metal layer 13 is laminated with the metal layer 11.

The support substrate 12 is conductive so as to ensure conductionbetween the bonding pad 15 and the backside electrode 14. For example,the support substrate 12 can be a silicon substrate, which isinexpensive and also easy to process. Other alternative substratematerials include Ge, InP, GaP, GaAs, GaN, and SiC.

Upon injection of a current into the light emitting layer 4 b throughthe bonding pad 15 and the backside electrode 14, light is emitted fromthe light emitting layer 4 b. The light emitted from the light emittinglayer 4 b toward the light extraction surface is extracted from thelight extraction surface to the outside of the device. The light emittedfrom the light emitting layer 4 b to the side opposite to the lightextraction surface is reflected toward the light extraction surface atthe interface between the semiconductor layer (lower current diffusionlayer 5) and the insulating film 8 and extracted to the outside of thedevice.

Next, an example method for manufacturing a semiconductor light emittingdevice according to this embodiment is described with reference to FIGS.4 to 6, in which the light emitting layer 4 b and the cladding layers 4a and 4 c shown in FIG. 1 are collectively shown as the light emittinglayer 4.

First, as shown in FIG. 4A, a contact layer 2, a current diffusion layer3, a light emitting layer 4, a current diffusion layer 5, and a contactlayer 6 are epitaxially grown in this order on a substrate 1. Thesubstrate 1 is suitable to good epitaxial growth of the above layers,and can be illustratively made of GaAs for an InGaAlP-based lightemitting device, and sapphire or SiC for a GaN-based light emittingdevice.

Next, as shown in FIG. 4B, the contact layer 6 is selectively etchedusing a mask 7, which is illustratively a silicon oxide film formed onthe contact layer 6. Thus, as shown in FIG. 4C, the contact layer 6 ispatterned in an island configuration. While only one contact layer 6 isshown in this figure, a plurality of contact layers 6 in an islandconfiguration are left on the current diffusion layer 5 with aprescribed pitch. Because the current diffusion layer 5 is not etched,current diffusion is not impaired by the patterning of the contact layer6.

Next, as shown in FIG. 5A, an insulating film 8 is formed on the currentdiffusion layer 5 to cover the contact layer 6. Then, a mask 9 is usedto etch away the insulating film 8 on the contact layer 6. Thus, asshown in FIG. 5B, the contact layer 6 is exposed. The opening 8 a formedby this etching of the insulating film 8 corresponds to the opening 8 ashown in FIG. 3.

The insulating film 8 is illustratively a silicon oxide film formed byCVD (chemical vapor deposition). Other alternative insulating materialsinclude a silicon nitride film and a silicon oxynitride film.Furthermore, the insulating film 8 can also be formed by evaporation orsputtering.

Next, as shown in FIG. 5C, a metal layer 11 is formed to cover thecontact layer 6 and the insulating film 8. The contact layer 6 is inohmic contact with the metal layer 11. The structure thus obtained islaminated with a support.

As shown in FIG. 6A, the support includes a support substrate 12 and ametal layer 13 formed on one surface thereof. The metal layer 11 and themetal layer 13 are desirably made of a material containing gold (Au).

Subsequently, the substrate 1 used for epitaxial growth of thesemiconductor layer including the light emitting layer 4 is removedillustratively by wet etching (FIG. 6B). In the case of quaternarysystems such as InGaAlP like this embodiment, typically, the substrate(e.g., GaAs substrate) suitable for epitaxial growth of thesemiconductor layer including the light emitting layer 4 highly absorbsthe light emitted from the light emitting layer 4. Removal of such asubstrate from the light extraction surface side increases theefficiency of extracting light to the outside of the device.

Subsequently, as shown in FIG. 6C, the contact layer 2 formed on thesurface of the current diffusion layer 3 on the light extraction surfaceside is selectively etched away for patterning, and a bonding pad 15 isformed on the remaining contact layer 2. Furthermore, a backsideelectrode 14 is formed on the backside of the support substrate 12.

A reflection type semiconductor light emitting device, which has astructure allowing the light emitted from the light emitting layer to betotally reflected at an insulating film, may be configured as shown in acomparative example of FIG. 11A. In this comparative example, a contactlayer 6 is provided on the entire surface of the semiconductor layer 25including the light emitting layer, and then an insulating film 8 isformed on the contact layer 6, which is left on the entire surfacewithout being patterned. Also in this case, to ensure ohmic contactbetween the contact layer 6 and the metal layer 11, an opening is formedin the insulating film 8 to selectively expose the contact layer 6 asshown in FIG. 11B.

In the structure of this comparative example, the contact layer 6 ispresent throughout the interface in the in-plane direction between theinsulating film 8 and the semiconductor layer 25 including the lightemitting layer. Hence, as shown by path a in FIG. 11B, the light emittedfrom the light emitting layer toward the insulating film 8 istransmitted through the contact layer 6, reflected at the insulatingfilm 8, and again transmitted through the contact layer 6 toward thelight extraction surface. Thus, the light reflected at the insulatingfilm 8 passes twice through the contact layer 6.

Typically, the material of the contact layer 6 suitable for ensuringgood ohmic contact between the metal layer 11 and the semiconductorlayer 25 including the light emitting layer highly absorbs the lightemitted from the light emitting layer. Consider an example in which thelight emitting layer is made of InGaAlP, the contact layer 6 is made ofGaAs, and the light emitting layer emits light at a wavelength of 630nm. The absorption coefficient at this wavelength is 319 mm⁻¹ for thelight emitting layer, but as large as 2823 mm⁻¹ for the contact layer 6.Hence, if the contact layer 6 is present throughout the interfacebetween the semiconductor layer 25 and the insulating film 8, the lightemitted toward the insulating film 8 is predominantly absorbed in thecontact layer 6, and this optical absorption in the contact layer 6decreases the brightness.

In contrast, in the semiconductor light emitting device according tothis embodiment described above, the contact layer 6 is selectivelyformed, and the insulating film 8 is formed at a position notoverlapping the contact layer 6. Thus, in this structure, the contactlayer 6 with high absorption of light emitted from the light emittinglayer is not present between the insulating film 8 and the semiconductorlayer (current diffusion layer 5).

In view of the efficiency of current injection into the light emittinglayer, the minimum requirement for the total area of the contact layer 6is determined. While this contact area is ensured, the insulating film 8is provided in the other portion. Thus, while optical absorption by thecontact layer 6 is minimized, the area of reflection at the insulatingfilm 8 without the intermediary of the contact layer 6 is increased toenhance the reflection efficiency. Consequently, the brightness can beincreased.

The light reflectance can be made higher by using an insulating film forthe reflecting layer than by using a metal. For example, the insulatingfilm 8 implemented as a silicon oxide film enables total reflection. In90% by volume of the incident hemisphere, a reflectance of 100% can beachieved in theory.

In contrast to the contact layer 6 formed on the entire surface as inthe comparative example, a sample having the structure of thisembodiment (the spacing between the contact layer 6 and the openinginner edge of the insulating film 8 is 2.5 μm) was prototyped so thatthe area ratio of the contact layer 6 is 6%, and was compared inbrightness with the comparative example. Then, the sample having thestructure of this embodiment delivered approximately twice thebrightness relative to the comparative example.

For uniform and efficient current injection throughout the lightemitting layer, it is preferable that the contact layer 6 be uniformlypresent in the in-plane direction. However, the portion below thebonding pad 15 does not serve as a light extraction surface, and doesnot contribute much to the light extraction efficiency, or brightness,even if the efficiency of current injection into the underlying lightemitting layer is increased. Hence, in the example shown in FIG. 1, thecontact layer 6 is not provided below the bonding pad 15.

In the embodiment described above, the interface between the contactlayer 6 and the current diffusion layer 5 is generally flush with theinterface between the insulating film 8 and the current diffusion layer5, and the insulating film 8 is thicker than the contact layer 6. Hence,the insulating film 8 protrudes from the contact layer 6 toward themetal layer 11. However, this invention is not limited to thisstructure. Alternatively, as shown in FIG. 7, the contact layer 6 can bethicker than the insulating film 8 and protrude therefrom toward themetal layer 11.

The metal layer 11 is formed to cover both the contact layer 6 and theinsulating film 8 after they are formed. Hence, the shape of the metallayer 11 reflects the step difference between the contact layer 6 andthe insulating film 8. As shown in FIGS. 1 and 2, if the contact layer 6is recessed relative to the insulating film 8, the metal layer 11 belowthe contact layer 6 is recessed toward the contact layer 6, and themetal layer 11 below the insulating film 8 protrudes toward the metallayer 13. Conversely, as shown in FIG. 7, if the contact layer 6protrudes from the insulating film 8, the metal layer 11 adjacent to thecontact layer 6 protrudes toward the metal layer 13.

It is noted that, if the contact layer 6 has the same thickness as theinsulating film 8, protrusions and depressions are scarcely formed inthe metal layer 11, which can be favorably laminated with the metallayer 13 in a wide area. However, process controllability with highaccuracy is required to form the contact layer 6 and the insulating film8 with the same thickness at non-overlapping positions on thesemiconductor layer surface. In contrast, in the structure of theinsulating film 8 projected from the contact layer 6, good pressurebonding is achieved by a simple process. Furthermore, in the structureof the insulating film 8 projected from the contact layer 6, thepressure at the time of lamination is transferred to the wafer throughthe insulating film 8, and hence the pressure applied to the wafer canbe alleviated.

FIGS. 8 and 9 show another example method for manufacturing asemiconductor light emitting device according to this embodiment.

In this example, after a contact layer 6 is formed on the entire surfaceof the current diffusion layer 5, a cap layer 21 is further formed onthe entire surface of the contact layer 6. Subsequently, by selectivelyetching the contact layer 6 and the cap layer 21 using the same mask, orby selectively etching the cap layer 21 and then selectively etching thecontact layer 6 using the cap layer 21 as a mask, a structure as shownin FIG. 8A is obtained, in which the cap layer 21 is provided on thepatterned contact layer 6.

The cap layer 21 has an etching selectivity with respect to the contactlayer 6 and the insulating film 8. For example, in the case where thecontact layer 6 is made of GaAs and the insulating film 8 is a siliconoxide film, the cap layer 21 can be made of a silicon nitride film orInGaP.

Next, as shown in FIG. 8B, an insulating film 8 is formed on the currentdiffusion layer 5 to cover the contact layer 6 together with the caplayer 21. Then, as shown in FIG. 8C, the insulating film 8 is etchedback halfway through the cap layer 21. At this time, it is importantthat the cap layer 21 and the insulating film 8 are processed at anearly equal etching rate. For example, in the case where the insulatingfilm 8 is a silicon oxide film and the cap layer 21 is a silicon nitridefilm, RIE (reactive ion etching) processing using a gas systemcontaining CF₄, SF₆, CHF₃, and O₂ is effective.

Subsequently, the cap layer 21 is selectively removed. Thus, a structureas shown in FIG. 9A is obtained, in which the upper surface of thecontact layer 6 is exposed with the contact layer 6 recessed relative tothe insulating film 8.

Subsequently, as shown in FIG. 9B, a metal layer 11 is formed to coverthe contact layer 6 and the insulating film 8. Then, as shown in FIG.9C, the metal layer 11 is laminated with a metal layer 13. Subsequently,steps similar to those of FIG. 6B and the following figures describedabove are performed.

In this example, the insulating film 8 is simply etched back throughoutits surface without being patterned. Hence, it is possible to eliminatethe clearance between the side surface of the contact layer 6 and theinsulating film 8 due to positional misalignment of the etching maskused in patterning the insulating film 8.

As shown in FIG. 6C, the metal layer 11 is provided in the clearancebetween the side surface of the contact layer 6 and the insulating film8. In this portion, instead of the insulating film 8, the metal layer 11serves as a reflecting layer. Comparing the case of no clearance betweenthe side surface of the contact layer 6 and the insulating film 8 withthe case where the clearance exists, if the area of the contact layer 6is equal, the existence of the clearance effectively reduces the area ofthe insulating film 8. Hence, as the clearance becomes smaller, the areaof reflection at the insulating film 8, which allows higher reflectancethan the metal layer 11, can be increased to enhance the brightness.

When the contact layer 6 is patterned, the cross section of the contactlayer 6 typically tends to be shaped like a mesa as shown in FIG. 10 dueto the plane orientation dependence of etching. In the process of FIGS.5A and 5B, the insulating film 8 is formed to cover the contact layer 6,and then selectively removed above the contact layer 6 to expose thecontact layer 6. At this time, if the insulating film 8 is removed onlyto position A shown by the dot-dashed line in FIG. 10, leaving part ofthe insulating film 8 on the tapered surface 6 a of the contact layer 6,then a projection 50 is formed at the upper surface of the insulatingfilm 8. The existence of this projection 50 may cause failure oflamination between the metal layer 11 formed on the insulating film 8and the metal layer 13 formed on the support substrate 12, and thus isundesirable.

Hence, to avoid leaving the insulating film 8 on the tapered surface 6 aof the contact layer 6, the insulating film 8 needs to be etched to agreater extent than the lower edge of the taper of the contact layer 6,illustratively to position B shown by the dot-dot-dashed line in FIG.10.

The required width of spacing (clearance) between the contact layer 6and the insulating film 8 surrounding its periphery is dictated by theetching shape of the contact layer 6. In the case where the contactlayer 6 is shaped like a mesa as shown in FIG. 10, it is undesirablethat the insulating film 8 is left on the tapered surface 6 a asdescribed above. Hence, the width of the tapered surface 6 a of thecontact layer 6 (the in-plane distance between the taper top and thetaper bottom) is the minimum required width of the above clearance. Forthe shape in which the side surface of the contact layer 6 is generallyperpendicular to the major surface of the underlying layer, the aboveclearance is desirably eliminated from the viewpoint of enhancing thereflectance by increasing the area of the insulating film 8. Inpractical manufacturing, the above clearance needs to be determined byalso considering process controllability and variations. As the resultof the inventors' study, it was found that the minimum required width ofthe clearance is desirably 0 or more and 10 micrometers or less.

Furthermore, the inventors made current distribution simulation for thedevice structure with the above contact layer 6 selectively formed, andobtained the result that the current density was increased in theportion of the light emitting layer directly above the contact layer 6(the portion facing the contact layer 6). Specifically, in the range ofapproximately 1.85 times the width of the contact layer around the lightemitting layer directly above the contact layer 6, the current densityin the light emitting layer was higher than the other region.

The region with high current density is a region with a large amount oflight emission. FIG. 12 schematically shows the region with a largeamount of light emission as a main light emitting region 100. In thecase where the insulating film 8 is made of SiO₂ and the currentdiffusion layer 5 is made of InGaAlP, for example, the condition thatthe light emitted from the main light emitting region 100 toward theinsulating film 8 is totally reflected at the interface between theinsulating film 8 and the semiconductor layer (current diffusion layer5) is that the incident angle of light with respect to the aboveinterface is 26° (critical angle) or more.

The light incident on the above interface at an incident angle largerthan the critical angle is totally reflected at the interface. However,the light from the main light emitting region 100 does not necessarilyundergo total reflection throughout the above interface. Morespecifically, in the light emitted from the main light emitting region100, the light component reaching the insulating film 8 with theshortest path is perpendicular to the above interface. Hence, in theportion of the insulating film 8 close to the contact layer 6 (theportion facing the main light emitting region 100), the light componentwith an incident angle smaller than the critical angle increases. Asschematically shown by an arrow in FIG. 12, the light incident on theinsulating film 8 at an angle smaller than the critical angle istransmitted through the insulating film 8 and reflected at the metallayer 11 underlying the insulating film 8. That is, in the surroundingportion of the contact layer 6, the light emitted from the main lightemitting region 100 is not totally reflected at the insulating film 8,but transmitted through the insulating film 8 and reflected at the metallayer 11 therebelow. Thus, there is concern about brightness decreasedue to the decrease of reflection efficiency.

Hence, according to a second embodiment of the invention shown in FIG.13, in the surrounding portion of the contact layer 6 where the lightemitted from the main light emitting region 100 is difficult to betotally reflected, the insulating film 8 is not formed, but a highlyreflective material 31 is provided therein. FIG. 13A shows thecross-sectional structure of the contact layer 6 and its surroundingportion, and FIG. 13B shows the planar layout of the contact layer 6 andthe highly reflective material 31.

Here, the metal layer 11, being responsible for bonding when thesemiconductor structure including the light emitting layer 4 islaminated with the support substrate, illustratively has a laminatedstructure of Ti, Pt, and Au. The surface of the metal layer 11 bonded tothe insulating film 8 is illustratively made of Ti to ensure goodadhesiveness with the insulating film 8. On the other hand, the surfaceof the metal layer 11 pressure-bonded to the metal layer 13 on thesupport substrate 12 side in the above step of FIG. 6A is made of Au forAu—Au bonding with the metal layer 13.

Because the insulating film 8 is not formed in the surrounding portionof the contact layer 6, a clearance is formed between the contact layer6 and the insulating film 8. Hence, if the metal layer 11 is formed tocover the insulating film 8 and the contact layer 6 in the above step ofFIG. 5C, the metal layer 11 is inserted into the above clearance. Here,in the example of the metal layer 11 of the above-described structure,Ti is used on the insulating film 8 side. Hence, the portion of themetal layer 11 in contact with the current diffusion layer 5 is made ofTi.

Ti has good adhesiveness with the insulating film 8 and thesemiconductor layer. However, the reflectance of Ti with respect tolight at a wavelength of approximately 630 to 640 nm, which is emittedillustratively from the InGaAlP-based light emitting layer 4, is as lowas 0.333.

Thus, in this embodiment, a highly reflective material 31 is provided inthe clearance portion between the insulating film 8 and the contactlayer 6. The highly reflective material 31 is at least in contact withthe current diffusion layer 5. The highly reflective material 31 is madeof a material having a higher reflectance with respect to the lightemitted from the light emitting layer 4 than the portion (Ti) of themetal layer 11 being in contact with (the backside 8 b of) theinsulating film 8. The highly reflective material 31 can beillustratively made of AuZn (the reflectance with respect to the lightemitted from the light emitting layer 4 is 0.896), Au (the reflectancewith respect to the light emitted from the light emitting layer 4 is0.97), and transparent electrode materials, including ITO.

Thus, according to this embodiment, the light emitted from the mainlight emitting region 100 to the side opposite to the light extractionsurface is reflected by the highly reflective material 31 in thesurrounding portion of the contact layer 6, and is totally reflected bythe insulating film 8 in the portion where incidence of light componentswith an incident angle larger than the critical angle increases.Consequently, the amount of reflection of the light emitted from themain light emitting region 100, which is a region with a large amount oflight emission, toward the light extraction surface can be increased toenhance the brightness.

The width of the clearance formed between the contact layer 6 and theinsulating film 8, that is, the range being devoid of the insulatingfilm 8 and provided with a highly reflective material 31, needs to beappropriately designed. Spreading the highly reflective material 31unnecessarily to the region allowing total reflection at the insulatingfilm 8 results in decreasing the amount of reflected light. Hence, thehighly reflective material 31 needs to be limited to a minimum requiredregion (width) where the effect of total reflection at the insulatingfilm 8 cannot be expected.

As the result of the inventors' study, it was found that the range ofthe highly reflective material 31 formed around the contact layer 6 (thewidth of the highly reflective material 31) b is desirably twice or lessthe width a of the contact layer 6. Under this condition, lightreflection in the portion not allowing total reflection at theinsulating film 8 is compensated by the highly reflective material 31while making best use of the effect of total reflection at theinsulating film 8, which accounts for a large part of the total area ofthe reflecting surface. Thus, this condition is effective in increasingthe brightness. More specifically, in consideration of the currentdevice design, process controllability, and process variations, it wasfound that the width of the highly reflective material 31 (the clearancewidth between the contact layer 6 and the insulating film 8) isdesirably 10 micrometers or less.

FIG. 14 shows an example method for manufacturing the structure shown inFIG. 13.

Also in this embodiment, the insulating film 8 is formed on the currentdiffusion layer 5 to cover the contact layer 6 by the above steps ofFIGS. 4A to 5A. Then, as shown in FIG. 14A, the insulating film 8 isselectively etched away using a mask 9 to expose the contact layer 6.Furthermore, by this etching, the insulating film 8 in the surroundingportion of the contact layer 6 is also removed to form a clearance cbetween the contact layer 6 and the insulating film 8.

Next, with the mask 9 left on the insulating film 8, a highly reflectivematerial 31 is formed illustratively by evaporation. Thus, as shown inFIG. 14B, the highly reflective material 31 is formed on the mask 9, onthe contact layer 6, and on the current diffusion layer 5 exposed to theclearance c.

Next, the mask 9 is removed together with the highly reflective material31 formed thereabove from above the insulating film 8 (lift-off). Asshown in FIG. 14C, the highly reflective material 31 is left on thecurrent diffusion layer 5 between the insulating film 8 and the contactlayer 6 (clearance c) and on the contact layer 6. In the example shownin FIG. 14, the highly reflective material 31 on the contact layer 6 isleft unchanged. Alternatively, for example, it can be etched away.

Next, as shown in FIG. 14D, the metal layer 11 is formed to cover theinsulating film 8, the highly reflective material 31, and the contactlayer 6. Subsequently, like the embodiment described above withreference to FIG. 6, a support substrate 12 is laminated by pressurebonding the metal layer 11 to a metal layer 13, and then the substrate 1used for epitaxial growth of the semiconductor layer including the lightemitting layer 4 is removed. Furthermore, by the steps of processing thecontact layer 2 on the light extraction surface side, forming a bondingpad 15, and forming a backside electrode 14 on the backside of thesupport substrate 12 are performed, and a semiconductor light emittingdevice according to this embodiment is obtained.

The embodiments of the invention have been described with reference tothe examples. However, the invention is not limited thereto, but can bevariously modified in accordance with the spirit of the invention.

The material of each component is not limited to that described above,but other materials can be used. For example, the light emitting layercan be made of GaN-based materials. Furthermore, in accordance with thematerial of the light emitting layer, the material of the contact layercan also be suitably selected from GaAs, AlGaAs, AlGaN, GaN and thelike.

With regard to the p-side electrode, instead of providing a backsideelectrode 14 on the backside of the support substrate 12, it is alsopossible to provide a region of the metal layer 13 on which theinsulating film 8 and the semiconductor layer including the lightemitting layer are not provided, and a bonding pad can be provided onthe metal layer 13 in that region. In this case, the support substrate12 can be non-conductive. Furthermore, the upper current diffusion layerand the lower current diffusion layer are not necessarily needed in thesemiconductor layer including the light emitting layer.

FIG. 15A is a schematic plan view showing an example electrode patternprovided on the light extraction surface side in the semiconductor lightemitting device according to the embodiments of the invention.

In this example, an electrode pad (bonding pad) 15 and a contact layer 2(see FIG. 1, for example) illustratively shaped like a circle areprovided at the center on the surface of the semiconductor layer (in thepresent embodiments, for example, the upper current diffusion layer 3).The contact layer 2 can be formed by a patterning technique using theelectrode pad 15 as a mask after forming the electrode pad 15 thereon.Alternatively, the contact layer 2 can be formed first by a patteringtechnique using appropriate mask such as a resist layer, then theelectrode pad 15 can be formed on the contact layer 2.

FIG. 15B is a schematic plan view showing another example electrodepattern provided on the light extraction surface side.

In this example, an electrode pad (bonding pad) 15 and a contact layer 2illustratively shaped like a circle are provided at the center on thesurface of the upper current diffusion layer 3, and a fine wireelectrode 41 and a contact layer 2 connected to the electrode pad 15 andthe contact layer 2 is further provided therearound. The fine wireelectrode 41 is laid out evenly throughout the surface of the uppercurrent diffusion layer 3. This structure is effective in evenlydiffusing the current in the in-plane direction particularly for a largechip size.

The metal material (not limited to pure gold, but also including alloys)constituting the electrode pad 15 and the fine wire electrode 41 isimpervious to light. The portion provided therewith does not serve as alight extraction surface, and improvement of light extraction efficiencycannot be expected even if the efficiency of current injection into thedirectly underlying light emitting layer is increased. Hence, thecontact layer 6 described above is not formed directly below theelectrode pad 15 and the fine wire electrode 41. That is, the patternconfiguration of the electrode pad 15, the fine wire electrode 41, andthe contact layer 6 is designed so that the contact layer 6 does notoverlap the electrode pad 15 and the fine wire electrode 41.

1. A semiconductor light emitting device comprising: a semiconductorlayer having a lower surface and including a light emitting layer; acontact layer selectively provided in contact with the lower surface; aninsulating film provided in contact with the lower surface so as tosurround the contact layer and be spaced apart from the side surfaces ofthe contact layer; a transparent material provided between the contactlayer and the insulating film, the transparent material in contact withthe sides of the insulating and the contact layer and in contact withthe lower surface, the transparent material having transparency withrespect to the light emitted from the light emitting layer; and a metallayer provided below and covering the contact layer, the insulating filmand the transparent material; and a support substrate provided below themetal layer.
 2. The semiconductor light emitting device according toclaim 1, wherein the insulating film is thicker than the contact layerand protrudes toward the metal layer.
 3. The semiconductor lightemitting device according to claim 1, wherein the width of thetransparent material is equal to or less than twice the width of thecontact layer.
 4. The semiconductor light emitting device according toclaim 1, wherein the transparent material contains ITO.
 5. Thesemiconductor light emitting device according to claim 1, wherein aninterface between the transparent material and the metal layer hashigher reflectance with respect to the light emitted from the lightemitting layer than an interface between the contact layer and thesemiconductor layer.